Belief that protection from smallpox resulted from infection acquired from cows

Jenner observed that some with history of cowpox “resisted” variolation

Jenner’s Experiment

Transferred “matter” from the hand of an infected dairymaid to 8 year-old James Phipps on 14 May 1796

Variolation unsuccessful on 1 July 1796

Phipps did not respond to variolation 5 years after original vaccination

Vaccination

Jenner’s observations soon reproduced by others

Practice quickly spread throughout Europe

Benjamin Waterhouse performed first vaccinations in U.S. in Boston, 1800

Smallpox Vaccine

Until the mid-19th century vaccine was generally transferred from arm-to-arm

Also distributed dried using threads, ivory points, or glass slides

Cows first used in Italy in early 19th century

“…it now becomes too manifest to admit of controversy, that the annihilation of the Small Pox, the most dreadful scourge of the human species, must be the final result of this practice.”-Edward Jenner, 1801Smallpox Vaccine

Original material used by Jenner was probably cowpox

Vaccine constituent changed from cowpox to vaccinia during the 19th century

Vaccinia Virus

Origin of vaccinia virus unknown

Genetically distinct from cowpox and variola

May be a virus now extinct in nature

Vaccinia Virus

Multiple strains with different levels of virulence for humans and animals

U.S. vaccine (Dryvax, Wyeth Laboratories) contains New York City Board of Health strain

Vaccine Production

Virus grown on skin of calves, sheep, and water buffalo

Material from lesions harvested before crusting to maximize viral titer

Pulp ground and originally mixed with 40%-60% glycerol and distributed in glass capillary tubes

Smallpox (Vaccinia) Vaccine

15 million doses now in stock

100-dose vials

Contract for additional 54 million doses produced on cell culture media

Response to Vaccination

Neutralizing antibody:

10 days after primary vaccination

7 days after revaccination

Considered fully protected after a successful response demonstrated at vaccination site

Vaccine Efficacy

Clinical efficacy estimated in household contact studies

91%-97% reduction in cases among contacts with vaccination scar

Studies did not consider time since vaccination or potency of vaccine

Post Exposure Vaccine Efficacy

Clinical efficacy estimated in household contact studies

SAR 2%-75%, varied by time since exposure

Disease generally less severe (modified type) in those with post exposure vaccination

55Contraindications for Vaccination of ContactsNONEIn general, the risk of developing smallpox for face-to face contacts outweighs the risk of developing vaccine complications for those contacts with contraindications to vaccination.56Vaccination of Contacts of Contacts

Household members of a contact without contraindications

Household members of a contact with contraindications, who are not vaccinated, must avoid the contact (18 days)

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